The subject of this project is the hormonal regulation of cyclic nucleotide levels and cyclic nucleotide phosphodiesterase activity, with special emphasis on cyclic guanosine 3',5'-monophosphate (cGMP). The effect of the steroid dexamethasone on cyclic guanosine monophosphate levels and cyclic guanosine monophosphate phosphodiesterase activity in HTC tissue culture cells and rat liver and other organs is under investigation.